This invention relates to an electron-beam generating apparatus comprising a support member (spacer) and an image forming apparatus such as a display device, to which the electron-beam generating apparatus is applied to and, more particularly to an electron-beam generating apparatus comprising a large number of electron-emitting devices and an image forming apparatus using the electron-beam generating apparatus.
[Description of Related Art]
Generally, an image forming apparatus has an outer casing maintaining vacuum status, an electron source for emitting electrons and its driver, an image forming portion having a fluorescent member which emits light by collision of electrons or the like, an acceleration electrode for accelerating the electrons toward the image forming portion and its high-voltage power source. In an image forming apparatus having a flat outer casing such as a thin-type image display device, a support member (spacer) is employed to obtain atmospheric-pressure-proof structure.
Conventionally, a cold cathode electron-emitting device is known as the electron-emitting device used in an electron source of an image forming apparatus. The cold cathode electron emitting device includes a field emission (hereinafter abbreviated to "FE") type device, a metal/insulating-layer/metal type (hereinafter abbreviated to "MIM") device, or a surface-conduction emission type device.
Known examples of the FE type electron-emitting devices are described by W. P. Dyke and W. W. Dolan, "Field Emission", Advance in Electron Physics, 8, 89 (1956) and by C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47,5248 (1976).
A known example of the MIM type electron-emitting devices is described by C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32,646 (1961).
A known example of the surface-conduction emission type electron-emitting devices is described by, e.g., M. I. Elinson, "Radio Eng. Electron Phys., 10, 1290 (1965).
The surface-conduction emission type electron-emitting device utilizes a phenomenon where electron-emission is produced in a small-area thin film formed on a substrate, by passing a current parallel to the film surface. As the surface-conduction emission type electron-emitting devices, electron-emitting devices using an SnO2 thin film according to Elinson mentioned above, an Au thin film according to G. Dittmer ("Thin solid Films", 9,317 (1972)), an In2O3/SnO2 thin film according to M. Hartwell and C. G. Fonstad ("IEEE Trans. ED Conf.", 519 (1975)), a carbon thin film according to Hisashi Araki et al. ("Vacuum", vol. 26, No. 1, p. 22 (1983))are reported.
FIG. 20 shows the structure of the abovementioned device by M. Hartwell and Fonstad as a typical example of these surface-conduction emission type electron-emitting devices. In FIG. 20, numeral 3001 denotes a substrate; and 3002, a conductive thin film comprising a metal oxide thin film formed by sputtering on an H-shaped pattern. An electron-emitting portion 3003 is formed by electrification process referred to as "forming" to be described later.
Conventionally, in these surface-conduction emission type electron-emitting devices, it is general to form the electron-emitting portion by electrification process "forming" on the conductive thin film prior to electron emission. That is, the forming processing is forming the electron-emitting portion with electrically high-resistance by application of a predetermined voltage to the both ends of the conductive thin film to partially destroy or deform the thin film. Note that in FIG. 20, as the electron-emitting portion 3003, the-destroyed or deformed part of the conductive thin film 3002 has a fissure, and electron emission is made around the fissure. Hereinafter, the conductive thin film 3002 including the electrification forming-processed electron-emitting portion 3003 will be referred to as a thin film 3004 including the electron-emitting portion. The electrification forming-processed electron beam emits electrons from the electron-emitting portion 3003 by applying a predetermined voltage to the thin film 3004 and passing a current through the electron-emitting devices.
As an example of the electron source having the surface-conduction emission type electron-emitting devices, Japanese Patent Application Laid-Open No. 64-31332 discloses an electron source having numerous surface-conduction emission type electron-emitting devices, arranged in parallel lines, where both ends of each device are wire-connected.
The combination of the electron source having a plurality of electron beam with a fluorescent member as an image forming member which emits light (visible light) by emitted electrons from the electron source provides various image forming apparatuses. Especially, image display devices (e.g., U.S. Pat. No. 5,066,883 by the present applicant) can be easily applied to a large-display screen devices, and can provide excellent display quality as voluntary light-emitting devices. Accordingly, these image forming apparatuses are expected to take the place of CRT display devices.
For example, in an image forming apparatus as disclosed in Japanese Patent Application Laid-Open NO. 2-257551 by the present applicant, selection of the electron beam is made by application of appropriate drive signals to wiring electrodes (row-direction wiring) connecting parallel arrays of surface-conduction emission type electron-emitting devices, and to wiring electrodes (column-direction wiring) connecting control electrodes arranged between the electron source and the fluorescent member in directions orthogonal to the above wiring directions.
As described above, in the recently proposed image forming apparatuses (flat type CRT's), cold cathode electron-emitting devices have been used for an electron source and support members (spacers) are incorporated for atmospheric-pressure-proof structure, so as to reduce the weight and depth of the apparatus.
However, in such flat type CRT's, disturbance of display image occurs around the support members. The considerable main cause is electric charge-up of the support members which may influence the trajectories of electrons. To prevent the electric charge-up, it has been arranged such that the support members which have conductivity has been considered.
However, the disturbance of display image cannot be fully corrected by merely providing the conductivity to the support members, and the shift of light-emission position, luminance degradation, change of color still occur around the support members.